Effect of UV-B radiation on chalcone syntase (CHS), isoflavone synthase (IFS) expression and flavonoid synthesis in common bean (Phaseolus vulgaris L.)

none6Common bean had been recognized since a long time for its protein content, but in general there have been relatively little research and discussion about the nutraceutical value of bean legumes. In common bean a number of flavonoids was isolated and identified. Earlier studies by our group showed that some Italian common bean ecotypes contained three glycosidic forms of the flavonoid kaempferol at the seed level and conspicuous amounts of isoflavones phytoestrogens (daidzein, genistein and glycitein), along with kaempferol, were detected in acid-hydrolyzed extracts of 2-3 day old seedlings. In Western world beans are widely consumed as seeds as a good source of protein and calories, while bean sprouts are traditionally consumed in some parts of Asia as food (especially soybean). However, in recent years there has been an increased consumption of sprouted legumes as vegetables (especially mungbean sprouts in Western Europe and America). Sprouting has often been proposed as a mean by which the nutritional quality of legume seeds might be improved, thanks to the breakdown of starch proteins and to the lowering of antinutritional factors. UV-B radiation (280-315 nm) has several effects on the physiology of terrestrial plants. Among these, the production of UV-B absorbing compounds, such as phenylpropanoids, including hydroxyl-cinnamic acid derivatives and flavonoids with effective absorption in the UV-B spectral region. Flavonoids can increase rapidly in response to UV-B radiation and are frequently found in or on epidermal layers. In the present study, one common bean cultivar, namely “Lingua di fuoco” (LDF), widely traded in Italy, and two common bean accessions from Zolfino from Pratomagno (Z1 and Z2) were screened for their response to UV-B radiation in the expression of two key enzymes of falvonoid and isoflavone biosynthetic pathway (chalcone synthase-CHS and isoflavone synthase-IFS), as well as on the synthesis of flavonoids. Five-days sprouts were subjected to UV-B treatment and compared to untreated sprouts. Different physiological responses in the expression of CHS and IFS were evidenced. LDF exhibited no overexpression of CHS and IFS mRNA. On the contrary, one Zolfino accessions (Z1) exhibited a fourfold overexpression 24 h after the treatment, while Z2 accession evidenced no overexpression. However, in Z2, CHS and IFS transcripts levels were 250-fold constitutively higher than those observed in LDF. As regards total flavonoid content, UV-B treatment did not elicit flavonoid synthesis in LDF, while in Z1 a conspicuous increase in flavonoid content was observed 24 h after the treatment. No significant increase of total flavonoid in Z2 accession was observed after UV-B exposure, probably for the high constitutive flavonoid amounts already present in not treated sprouts. Our results indicated the concrete chance to use common bean sprouts as source of nutraceutical compounds, such as daidzein, glycitein, genistein and kaempferol. In particular, Zolfino from Pratomagno sprouts exhibited, after UV-B elicitation, a flavonoid content comparable with that of soybean seedlings.noneDinelli G.; Marotti I.; Bonetti A.; Bosi S.; Busi S.; Catizone P.Dinelli G.; Marotti I.; Bonetti A.; Bosi S.; Busi S.; Catizone P